Hybrids have become the public perception of the pinnacle of efficiency, though they may become victims of their own success. A recent Reuters report details how hybrid sales growth is spurring fears of shortages in the rare earth elements market.

These fears of shortage have been aired in the past, but towards key battery elements lithium and nickel. However, now, with Toyota projecting sales of 100,000 units of its mild child this year, it's becoming increasingly important to look at the more unusual mined elements in a hybrid, where they're used, and how much of it it takes to make just a single Prius.

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Rare Earth Element: NeodymiumAmount per Prius: 1 kilogram (2.2 lb)Use: Powerful magnetic element used in compact electric motors. The shiny button magnets that keep little motors going an clasp clever covers. In large enough quantities, as in one kilo of magnet, there's plenty of force to crush your little piggies with great vengeance.Trouble: Neodymium is a magnificent material with a high magnetism to volume rating. So for every cubic something of neodymium, you get a great bang for the buck in magnetism compared to traditional magnets. It also means there's a lot of competition with the consumer electronics biz, which is in a brutal competition to modernize and micro-size any and all components, including magnet-based speakers, as a start. Add to that the recent surge in interest over wind power from turbines, which also use neodymium magnets, and you've got the makings of market trouble.

Rare Earth Element: Lanthanum.Amount per Prius: 10 to 15 kg (22-33 lb)Use: The intermetallic element in nickel-metal hydride batteries, the amount of lanthanum is proportional to the number of cells per battery. Also alloyed with neodymium to stabilize the high magnetic field.Trouble: The volume of material used in the Prius battery is only an estimate, but it puts into stark contrast the production capability of current suppliers. It's been estimated there's a total of 40,000 kg mined per year

The current mining giant is China as this graph representing rare earth element mining shows, however, it's difficult to say exactly how much material is being mined at any given time as there's no formal trading market. With the previous juggernaut of Mountain Pass planned to be reopened in some capacity in California in 2012, along with Avalon mines in Canada's Northwest Territories there will be additional supplies opening up, but only to the tune of about a 2-5% increase.

Not all of the 15 rare earth elements are appropriate for automotive use, only the two we've mentioned are used in any quantity along with terbium and dysprosium used in trace amount for alloying. Like other cars, the Prius grabs its fair share of precious metals like platinum, gold, silver, palladium as well as the common elements and refined petroleum products like plastics. When taken in context, a years worth of material to supply production for any mass market automobile takes on staggering proportions. Calling any car "green" over any other is an exercise in self-delusion, it's just that ironically, the "greenest" of publicly perceived cars is one that may drive some commodities markets to the brink.

(Thanks to Jack Lifton, independent commodities consultant and strategic metals expert, for assisting with this article)